While it is true that only legislatures can define crimes, courts give less deference to the legislative power in the criminal arena than in other areas. Whether that is due to the unique sanctions that criminal law carries (see Chapter 2 on punishment) is not clear. However, recognizing the interplay of these three sources—common law, statutes, and constitutional precepts—is essential to understanding American criminal law.
Law-abiding people should not have to guess at whether there is a criminal law forbidding their conduct or, if there is, what that law means. Likewise, the police, who enforce the law, should not have the power to decide what behavior the law covers. Finally, both trial and appellate courts need to know what the law is in order to apply it fairly and consistently in numerous cases.
Several doctrines, including the principle of legality, the constitutional doctrine of “void for vagueness,” and the rule of lenity, address these concerns. The principle of legality provides that before individuals can be convicted and punished for engaging in such conduct, it must be legislatively prohibited. The constitutional doctrine of void for vagueness requires the criminal law to be sufficiently clear so that individuals of ordinary ability can understand what their legal obligations are. The rule of lenity requires a court to construe criminal statutes strictly, resolving doubt in favor of the defendant.
The common law method of formulating new crimes virtually stopped in the mid-nineteenth century. Nonetheless, English judges still occasionally apply common law crimes to novel situations that are not expressly covered by a criminal statute. Thus, in Shaw v. Director of Prosecutions, the defendant published a “Ladies Directory” of prostitutes, which contained their names, pictures, addresses, and telephone numbers. Prostitution itself was not a crime, but soliciting in public was. The House of Lords upheld the defendant’s conviction for “conspiracy to corrupt public morals” even though there was no criminal statute forbidding the publication of such a directory. Viscount Simonds concluded that courts retained:
residual power to enforce the supreme and fundamental purpose of the law, to conserve not only the safety and order but also the moral welfare of the State….[I]t is their duty to guard against attacks which may be the more insidious because they are novel and unprepared for…. Such occasions will be rare, for Parliament has not been slow to legislate when attention has been sufficiently aroused. But gaps remain and will always remain since no one can foresee every way in which the wickedness of man may disrupt the order of society.